The long-term objective of this work is to understand the cell biological events that occur upon the onset, maintenance and breakdown of the symbiotic relationship between cnidarians (corals and sea anemones) and photosynthetic algae. The algae are phagocytosed from seawater and appear to evade the host immune response and alter subcellular trafficking to allow their intracellular persistence. The algae, of the genus Symbiodinium, use energy from sunlight to make sugars from carbon dioxide and water, and give up to 90% of this sugar to the coral or anemone host. This relationship is essential for the growth of corals and its breakdown, known as coral bleaching, can result in the collapse of entire reef ecosystems. This project examines the interactions between a model system, the sea anemone Nematostella vectensis, and Symbiodinium. Unlike many of its closely-related cousins, Nematostella is not naturally symbiotic. The interactions of Nematostella and Symbiodinium will be probed microscopically and by using full-genome microarrays to analyze transcriptional changes that occur upon challenge with Symbiodinium. Nematostella is the only salt-water cnidarian with full genomic sequence available, allowing a detailed and complete analysis of its transcriptional responses to challenge with Symbiodinium. These responses will be compared to the interaction of Nematostella with food or other microbes and also to the interaction of naturally symbiotic cnidarians to Symbiodinium. Genes with altered transcription become of immense interest in the evolution of self vs. nonself recognition (the innate immune response of the cnidarian host) as well as the regulation of intracellular trafficking. Finally, they represent potential targets for prevention of coral reef bleaching or for inhibition during infection of corals with heterologous Symbiodinium, which might be more suited to current environmental conditions. The expression of genes, which are up-regulated and may block symbiotic onset, will be selectively knocked down using morpholinos and the effects will be analyzed microscopically. The sponsor laboratory has utilized (and in many cases, developed) the approaches and techniques required for the completion of the goals of this proposal, while the applicant has little expertise in this area. The applicant will be trained by the sponsor and members of the sponsor's laboratory (including graduate students, post- doctoral fellows and research assistants). The applicant plans to continue aspects of this project at her home institution. Additionally, she will also utilize the techniques learned during this training period to address the cell biology of symbiosis in the naturally-symbiotic anemone, Aiptasia pallida. PUBLIC HEALTH RELEVANCE: This proposal analyzes the interaction between cnidarians and photosynthetic algae that is the basis for coral reef ecosystems. Reefs are already the source of a large number of biomedically-important compounds, and it is likely that more will be identified in the future if reef ecosystems survive anthropomorphic changes. In addition, analyzing the interaction between these organisms will likely give insight into the interaction of other animals (like humans) with intracellular eukaryotic parasites like Toxoplasma, Plasmodium and Cryptosporidium.